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MELSEC-Q
11 TROUBLESHOOTING
Special Relay List
(3) System clocks/counters
Number
Name
Meaning
Explanation
Set by
(When Set)
Corresponding
ACPU
M9
Applicable
CPU
SM400 Always ON
O
N
O
FF
• Normally is ON
S
(Every END
processing)
M9036
SM401 Always OFF
O
N
O
FF
• Normally is OFF
S
(Every END
processing)
M9037
SM402
ON for 1 scan
only after RUN
O
N
O
FF
1 scan
• After RUN, ON for 1 scan only.
• This connection can be used for scan execution type
programs only.
S
(Every END
processing)
M9038
SM403
After RUN, OFF
for 1 scan only
ON
OFF
1 scan
• After RUN, OFF for 1 scan only.
• This connection can be used for scan execution type
programs only.
S
(Every END
processing)
M9039
SM404
Low speed
execution type
program
ON for 1 scan
only after RUN
O
N
O
FF
1 scan
• After RUN, ON for 1 scan only.
• This connection can be used for low speed execution
type programs only.
S
(Every END
processing)
New
SM405
Low speed
execution type
program
After RUN, OFF
for 1 scan only
ON
OFF
1 scan
• After RUN, OFF for 1 scan only.
• This connection can be used for low speed execution
type programs only.
S
(Every END
processing)
New
SM409
0.01 second
clock
0.005 sec.
0.005 sec.
• Repeatedly changes between ON and OFF at 5-ms
interval.
• When PLC power supply is turned OFF or a CPU module
reset is performed, goes from OFF to start.
• Note that the ON-OFF status changes when the
designated time has elapsed during the execution of the
program.
S (Status
change)
New QCPU
SM410 0.1 second clock
0.05 sec.
0.05 sec.
M9030
SM411 0.2 second clock
0.1sec.
0.1sec.
M9031
SM412 1 second clock
0.5 sec.
0.5 sec.
M9032
SM413 2 second clock
1 sec.
1 sec.
• Repeatedly changes between ON and OFF at each
designated time interval.
• When PLC power supply is turned OFF or a CPU module
reset is performed, goes from OFF to start.
• Note that the ON-OFF status changes when the
designated time has elapsed during the execution of the
program.
S (Status
change)
M9033
SM414 2n second clock
n sec.
n sec.
• Goes between ON and OFF in accordance with the
number of seconds designated by SD414.
• When PLC power supply is turned OFF or a CPU module
reset is performed, goes from OFF to start.
• Note that the ON-OFF status changes when the
designated time has elapsed during the execution of the
program.
S (Status
change)
M9034 format
change
SM415 2n (ms) clock
n(ms)
n(ms)
• Switches between ON and OFF in accordance with the
number of milliseconds designated by SD415.
• When PLC power supply is turned OFF or a CPU module
reset is performed, goes from OFF to start.
• Note that the ON-OFF status changes when the
designated time has elapsed during the execution of the
program.
S (Status
change)
New QCPU
SM420
User timing clock
No.0
M9020
SM421
User timing clock
No.1
M9021
SM422
User timing clock
No.2
M9022
SM423
User timing clock
No.3
M9023
SM424
User timing clock
No.4
• Relay repeats ON/OFF switching at fixed scan intervals.
• When PLC power supply is turned OFF or a CPU module
reset is performed, goes from OFF to start.
• The ON/OFF intervals are set with the DUTY instruction.
DUTY n1 n2 SM420
S
(Every END
processing)
M9024
SM430
User timing clock
No.5
SM431
User timing clock
No.6
SM432
User timing clock
No.7
SM433
User timing clock
No.8
SM434
User timing clock
No.9
n2
scan
n2
scan
n1
scan
• For use with SM420 to SM424 low speed programs.
S
(Every END
processing)
New